View Full Version : SDO footage of moon transit across sun

2012-Feb-24, 02:49 AM
Hello I just recently saw the footage from SDO of the moon transiting across the sun and my question is at one part of the video it shows the moon going down and then going backup again.
Link to video

2012-Feb-24, 03:16 AM
The SDO is in geosynchronous orbit, with nearly 30 orbits per lunar orbit and an orbital diameter much larger than that of the moon. This isn't so much the moon going across the sun as the satellite briefly swinging partly behind the moon for part of its orbit. If the moon's shadow is tangent to the SDO's orbit, it'll duck briefly into the moon's shadow (with the moon thus covering part of the sun) before its orbit takes it back in the direction it came from.

2012-Feb-25, 09:20 PM
SDO is in geosychronous orbit, but not geostationary. Its orbit is inclined 51 degrees from the ecliptic plane. That means that once per orbit it will travel nearly 33,000 km above Earth and 33,000 km below Earth. This up/down motion will make any objects at a distance seem to move up and down. Here's an image of the date in question. It was generated with Gravity Simulator and JPL Horizons ephemeris for solar system bodies and spacecraft. The view is from SDO looking towards the Sun. You can see the Moon's path. It is not straight. It descends down upon the Sun, then rises again. Even Mars', Uranus', and Neptune's orbits show some parallax.